The present invention relates to a gas turbine engine combustion chamber.
In order to meet the emission level requirements, for industrial low emission gas turbine engines, staged combustion is required in order to minimise the quantity of the oxides of nitrogen (NOx) produced. Currently the emission level requirement is for less than 25 volumetric parts per million of NOx for an industrial gas turbine exhaust. The fundamental way to reduce emissions of nitrogen oxides is to reduce the combustion reaction temperature and this requires premixing of the fuel and all the combustion air before combustion takes place. The oxides of nitrogen (NOx) are commonly reduced by a method which uses two stages of fuel injection. Our UK patent no. 1489339 discloses two stages of fuel injection to reduce NOx. Our International patent application no. WO92/07221 discloses two and three stages of fuel injection. In staged combustion, all the stages of combustion seek to provide lean combustion and hence the low combustion temperatures required to minimise NOx. The term lean combustion means combustion of fuel in air where the fuel to air ratio is low i.e. less than the stoichiometric ratio.
The gas turbine engine combustion chamber in our UK patent no. 1489339 uses a tubular combustion chamber, whose axis is arranged substantially parallel to the axis of the gas turbine engine. The tubular combustion chamber has an annular secondary fuel and air mixing duct which surrounds the primary combustion zone. An annular fuel manifold is located within and at the upstream end of the annular secondary fuel and air mixing duct to inject fuel into the annular secondary fuel and air mixing duct.